Gaseous discharge lamps, and in particular fluorescent lamps, utilize a ballast circuit for initiating the lighting of a tube. In addition, the ballast circuit controls the distortion effects which can be caused by the such lights on the power supply. Several prior art ballast circuits are known.
A first prior art ballast circuit is termed a "preheat magnetic ballast" circuit which utilizes a magnetic coil in conjunction with a starter circuit for lighting the fluorescent tube. A 60 Hertz (Hz) AC signal is applied across the fluorescent tube, with one side of the circuit having the magnetic coil attached thereto. Current flows through the magnetic coil, through one of the filaments of the fluorescent tube, to a starter circuit. The current warms the filament in the tube while the starter circuit pulses the tube with a voltage in an attempt to initiate fluorescence.
The preheat magnetic ballast circuit has several deficiencies. First, this type of ballast circuit applies 60 Hz AC across the tube to power the light. This is inefficient as compared to using a high frequency AC signal (e.g. more than 10 kHz) used with electronic ballast circuits. When a fluorescent tube is powered with a signal of at least 10 kHz, the output of the fluorescent light will be 15-20% more than if the same tube is supplied with a standard 60 Hz AC signal with the same amount of power consumption.
In addition, the magnetic coil itself is inefficient, resulting in a high energy loss. Further, magnetic coils are bulky in size, heavy and also utilize a lot of raw materials. The voltage which is used by such a ballast circuit to light the tube after preheating is a high voltage. However, excessive voltage across the filaments results in reduced filament life, thereby reducing the life of the fluorescent tube.
High starting voltage causes electrons in the filament material to release from their atoms, causing a sputtering of the filament element. This can result in the familiar darkening at the ends of fluorescent tubes. Eventually, the filament will fail from the excessive voltage. Further, in this type of a ballast circuit, it may be necessary for the starter to pulse the fluorescent tube a number of times with high voltage before the tube lights. This is not only inefficient, but the repeated pulsing causes the filaments to decay more rapidly.
A second ballast circuit is known as a "rapid start ballast" which includes a transformer that constantly supplies the filaments of the fluorescent tube with a current. As such, the filaments of the tube are always maintained in a "warmed-up" condition which enables the lights to be rapidly lighted upon the application of the appropriate voltage. However, once the fluorescent tube is lighted, the transformer continues to supply the filaments with current. Thus, there is always power being supplied across the filaments of the fluorescent tube. Such a condition results in excessive energy waste.
The third type of ballast circuit is known as "instant start." The instant start circuit supplies the tube with an excessively high voltage at start up. Typical starter circuits utilize a voltage which is four to six times the typical operating voltage of the fluorescent tube. The instant start circuit is on the high end of this scale, and it is not uncommon to have a starting voltage as high as 1000 volts AC. While the voltage is high enough to ensure the lighting of the fluorescent tube, the high voltage is harmful to the filaments of the tube as discussed above. Indeed, such high voltage can result in a decrease in the life of the tube by 200% or more as compared to other ballast circuits which do not utilize excessively high voltages to initiate fluorescence.
Thus, there is a need for a ballast circuit having a starter which is energy efficient and which does not cause excessive wear of the filaments of the tube, is inexpensive, and does not have excessive weight.